The present invention relates to electrostatographic printing apparatus and more particularly to devices for detacking a copy sheet, onto which a toner image has been transferred from an imaging member, from the imaging member.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
Many commercial applications of the above process employ a modular concept for the various processing stations. For example, the imaging member, developer assembly and cleaner assembly may be combined in a single unit or cartridge which has a limited life at the end of which it may be discarded and replaced with a new unit or cartridge. Alternatively, a charging device may be added to the unit or the unit may contain either of the developer or the cleaner.
For example, U.S. Pat. No. 3,985,436 (Tanaka et al.) describes a copying apparatus in which an imaging member, developing device and cleaner may be incorporated in a casing as one unit to be releasably inserted into the main apparatus housing.
U.S. Pat. No. 4,470,689 (Nomura et al.) also describes such a unit which is provided with a movable protection cover for protecting the image bearing member and illustrates in FIGS. 15A-15F several different alternative of process elements which may be included in such a process unit.
In many commercial applications it is desirable to provide assistance in physically separating the copy sheet bearing the toner image from the imaging member since the copy sheet may be tacked to the imaging member and which if not separated, may enter the cleaner housing resulting in a paper jam, loss of copy and contamination of the machine by toner displaced from the cleaner.
Well known detacking devices include a device for detacking the paper from the photoreceptor by suction, a detacking belt for holding an edge of the copy paper away from the imaging member, self stripping suitable for photoreceptor belts where the belt goes around a very small radius and the beam strength of the paper separates it from the belt, and a device having a claw with its tip abutting the photoreceptor for detacking the paper.
However, the suction detacking device is large and expensive so that its applications are limited to very high volume machines despite its excellent detacking property. Similarly, the belt strip has excellent detacking reliability, but an edge of the copy paper is blanked out because of its contact with the belt, making faithful reproduction impossible. The self strip requires no special detacking means and is inexpensive, but it has poor detacking reliability especially for tracing paper that is very thin. The detacking device with a claw is less expensive than the other three types and is able to produce a faithful copy, and give satisfactory detacking reliability by selecting the proper shape, material, number, and mounting method of claws so that it is widely used today.